Piston ring and piston construction



Feb. 17, 1959 M. STERN PISTON RING AND PISTON CONSTRUCTION Filed Feb.11, 1957 This invention relates to pressure expandible piston rings fordie casting machines and the likeand to an improved combination ofpiston rings and piston construction for die casting machine pressurechambers, and for other purposes.

In die casting machines, molten metal is forced under pressure from amolten metal pot to a nozzle, leading to the die cavity of the castingmachine by means of a plunger or piston operating in a cylindricalpassage or pressure chamber disposed in the molten metal pot. With thetrend toward producing die castings with thinner walls andsmoothersurfaces, the pressures atwhich molten die cast metalisforcedthrough the nozzle of the die casting machine into the moldlhavebeen increased from time to time. The piston of the die casting machinemust be relatively tight fitting in respect to the cylindrical moltenmetal passage in which it operates. Die casting machine pistons forhandling molten metal are usually equipped with split type piston ringsof the type generally employed in internal combustion engines.

The life of ordinary split type piston rings for such use is notsatisfactory for several reasons. In the first place, oxides and othergritty compounds work their way'between the rings and the piston ringgrooves in the pistons with a result that a wedging action occurs whichofttimes prevents the normal and expected expansion and contraction ofthe piston rings. Secondly split type piston rings are not only subjectto extremely heavy loads when metal is forced into the die, but they arealso subject to abrasion and erosion during the return stroke of thepiston when molten metal is sucked into the molten metal passage betweenthe piston and the nozzle of the die casting machine from above thepiston to break the vacuum in such passage. Thirdly, extreme temperaturedifferentials cause the ends at the split of the ordinary splittypepiston rings to curl or warp, and, should such curled ends work aroundthe piston and become'in alignment with the port in the cylinder, thesaid ends willlsnap off and ofttimes cause irreparable damage to .eitherthe cylinder or the piston before thedefectcan be discovered.

With the foregoing in view, the primary object of the invention is toprovide an improved positive expanding and contracting continuous pistonring which will-alleviate or overcome the foregoing and otherundesirable features of split type piston rings for the molten metalpressure piston of die casting machines.

; Another object of the invention is to provide an improvedpiston-piston ring combination wherein, pressure offluid against.the'head of the piston expands the piston ring during .the powerstroke'of the piston to-eliminate to a greater degree than heretoforepracticable the leakage of .fluid past. the piston.

A further-object of the invention is to provide a pressure expandiblepiston ring adapted to expand radially during the pressure'stroke of apiston equipped therewith and be'freetocontractradially during thereturn stroke of the p ston-teramit flu ;a d t Pa b w en h .p

atent 2,874,012 Patented Feb. 17, 1959 '2 and wall of the cylinder inwhich the said piston is mounted during the return stroke of the piston.

Other objects of the invention will becometapparent by reference to thefollowing detailed description taken in connection with theaccompanyingdrawing, in which:

Fig. 1 is a more orless diagrammatic view of a die casting machine of atype in which thepiston of the cylindrical portion of the pressurechamber thereof may be equipped with a piston ring and piston embodyingthe invention.

Fig. 2 is a vertical sectional view through a piston ring and pistonembodying the invention disposed in operating position within itscylinder.

Fig. 3 is an end elevational view of the head of the piston shown in.Fig. 2,.a portion of its cylinder being indicated in sectiontherearound.

Fig. 4 is a verticahsectionalview similar to Fig. 2 of a piston ringand. piston disclosing an alternate embodiment of the invention. 1

Fig. 5 is an end 'elevational view of the head of the piston shown inFig.4, a portion of its cylinder being indicated in section therearound.

Fig. 6 is a vertical sectional view of a piston ring-and piston showingstill another embodimentof the invention.

Fig. 7 is an end elevational view of the piston shown in Fig. 6, aportion of its cylinder being indicated in section therearound.

Referring now to the drawing wherein like reference numerals refer tolike and corresponding parts throughout the several views. Fig. v1showsaidie casting machine 10 including a moltenmetal pot .11, apressure chamber 12 disposed in said molten mctalpot and having anozale13 at the discharge end thereof communicating with a die 14 mounted inthe said die castingmachine 10. The said pressure chamber 12 is formedwith cylinder 15 therein into which is reciprocatinglymounted a piston16 preferably actuated by a hydraulic cylinder 17. The cylinder 15 ofthe pressure chamberv 12 is provided with an intake port 150 disposedslightly below the head of the piston 16 when in its retracted positionas shown in Fig. l. Molten metal 18 flows into the pressure chamber-12from the molten metal pot'll between molding shots when the piston 16 isin its retracted position. The said piston 16 is preferably formed toaccommodate apiston ringQZO embodying the invention .as hereinafterdescribed .in detail. I

The embodiment of the invention shown, in Figs. 2 and 3 consists of acontinuousgenerally vU-shaped piston ring 20 disposed in acircumferential recess in the piston 16. The top and the bottom sidewalls of the said U-shaped piston ring 20 as viewed in Fig. 2 arepreferably flanged at 21. The bottom wall 22 of thesaid U-shaped pistonring 20 is preferably formed with'a groove 220 therearound adjacent thewall of the cylinder'lS topmvide a local axially central annular areathat may flex more readily than the remainder of the said piston ringThe said piston 16 .has a main portion 31 which cumferential groove 34near the bottom thereof. The said groove 34 divides the. stem. 32 into abarrel portion 320 and a head portion 321. The upper flange 21 of theU-shaped continuous piston ring 20 is telescoped neatly over the collar33 of the stem 32 of the piston 16 to locate the piston ring 20concentrically thereon and to provide a pressure seal between the upperflange 21 of the piston ring 20 and the main portion 3i of the saidpiston 16. A pair of substantially half cylindrical or arcuate pressureelements'35 are positioned around the head portion 3210f the stem 32 ofthe piston 16. The said arcuate pressure elements 35 each'have aninwardly disposedflange v359 extending into the circumferential groove34 in the said stem 32. The thickness of the said flange 350 of eacharcuate pressure element 35 is less than the width of the'circumferential groove 34 in the stem 32 of the piston 16 to permit thesaid arcuate pressure elements 35 to move axially with respect to thepiston 16. The internal radius of the flange 350 of each pressureelement 35 is preferably such as will provide a slight passage 351between the stem 32 of the piston 16 at the base of the circumferentialgroove 34 therein and the inner structure surface of the said flange 350of each pressure element 35.

When the piston ring 20 and the arcuate pressure elements 35 areassembled onto the stem 32 of the piston 16 as shown in Figs. 2 and 3,the arcuate pressure elements 35 are preferably in contact with thelower flange 21 of the U-shaped continuous piston ring 20, and thesaidpressure elements 35 are in an axially extended position disposedtoward or against the lower end or "head portion 321 of the stem 32 ofthe said piston 16. The said stem 32 of the piston 16 is axially boredat 322 from its lower end or ead 321, and its barrel portion 320 isradially bored at 323' to provide communication between the cylinderbelow the piston 16 and the annular pressure chamber 200 inside of thesaid continuous generally U-shaped piston ring 20. The passage 351between the base of the circumferential groove 34 in the piston 16 andthe'inner arcuate surfaces of the flanges 350 of the pressure elements35 communicates withthe annular space 210 betweenv the bottom flange 21of the piston 16 and the stem 32 of the said piston 16 to permit axialmovement of the arcuate pressure elements 35 with respect to the saidpiston 16 without entrapment of molten metal therebetween.

With the construction disclosed in Figs. 2 and 3, when the piston '16 ison its power stroke, pressure of molten metal on the head thereof(against 35 and 321) moves the pressure elements 35 axially upwardly inthe circumferential groove 34 in the axially depending stem 32 of thesaid piston 16 as viewed in Fig. 2, whereupon the end flanges 21 of thepiston ring are forced toward each other to bow the wall 22 of the saidpiston ring 20 outwardly into firm contact with the inner wall of thecylinder 15. At the same time, molten metal under pressure flows throughthe bores 322 and 323 of the piston 16 and enters the annular pressurechamber 200 between the inner face of the U-shaped piston ring 20 andthe stem 32 of the said piston 16 further urging the said wall 22 of thepiston ring 20 radially outwardly into a pressure contact with the saidinner wall of the cylinder 15. During the return stroke of the piston16, the pressure within the said annular pressure chamber 200 and thepressure on the pressure elements 35 is relieved, whereupon the wall 22'of the piston ring 20 may flex radially inwardly and permit moltenmetal to be sucked past the piston 16 and the piston ring 20 thereofwithout undue abrasion and erosion of the said piston ring 20 and thecylinder 15.

The embodiment of the invention shown in Figs. 4 and 5 consists of acontinuous generally U-shapcd piston ring 20 disposed in acircumferential recess 40 in the piston 160. The top and the bottom ofthe piston ring 20 as-viewed in Fig. 4 is preferably flanged at 21. Theouter wall 22 of the said piston ring 20 is preferably formed with agroove 220 therearound adjacent the wall of the cylinder 15 to provide alocal axially central annular area that may flex more readily than theremainder of the said piston ring wall. The said piston 160 has a mainportion 41 which is suitably machined to provide an axially dependingstem 42 having a collar 43 at the top thereof and a threaded shank 44 ofreduced diameter at the bottom thereof forming an axially facing annularseat 420 at the lower end of the said stem 42 adjacent its threadedshank 44. A bored and counterbored piston head 45 is telescoped-onto thesaid threaded shank 44 and is secured centrally onto the stem 42 by anut 46 with a lock washer 47 thcrebetween. The said piston h 45 and thestem 42 of the piston 'are'so mated'at the seat 420 that the said'pistonhead 45 is held concentrically with respect to the main portion 41thereof when the nut 46 is tightened.

When the piston ring 20 and the piston head 45 are assembled onto thestem 42 of the piston 16 as shown in Figs. 4 and 5, the upper portion ofthe said piston head 42 as viewed in Fig. 4 firmly contacts the lowerflange 21 of the U-shaped continuous piston ring 20. The said stem 42 ofthe piston 160 and the threaded shank 44 thereof are axially bored at422 and the said stem 42 is radially bored at 423 to providecommunication from the cylinder 15 below the piston 160 and the annularpressure chamber 200 inside the continuous generally U- shaped pistonring 20.

With the construction shown in Figs. 4 and 5, when the piston 160 is onits power stroke, pressure from molten metal at the head 45 thereofenters and flows through the bores 422 and 423 into the annular pressurechamber 200 between the inner face of the U-shaped piston ring 20 andthe stem 42 of the said piston 16 urging thewall 22 of the piston ring20 radially outwardly into a pressure contact with the inner wall of thecylinder 15. During the return stroke of the piston 16, the pressurewithin the said annular pressure chamber 200 is relieved, whereupon thewall 22 of the piston ring 20 may flex radially inwardly and permitmolten metal to be sucked past the piston 16 and the piston ring 20without undue abrasion and erosion of the said piston ring 20 and thecylinder 15.

The embodiment of the invention shown in Figs. 6 and 7 consists of acontinuous generally S-shaped piston ring 50 disposed in acircumferential recess 60 in the piston 1600. The said continuousS-shaped piston ring has an inner annular free wall 51 flanged at itsupper edge at 52, an outer annular free wall 53 having a depending edgeat 54, and a central annular Wall 55 con nected to the said free walls51 and 53 by curved portions forming contact annuli 56 and 57respectively. The said piston 1600 has a main portion 61 which issuitably machined to provide an axially depending stem 62 having acollar 63 at the top thereof and a plain shank 64 of reduced diameter atthe bottom thereof forming an axially facing annular seat 620 at thelower end of the said stem 62 adjacent its plain shank 64. 'A' centrallybored and counterbored piston head 65 is telescoped in axially slidablerelationship onto the said plain shank 64 and is held thereon by meansof a transverse pin 66 pressed into a round hole 650 in the piston headand extending through a vertically elongated hole 621 in the stem 62.The piston head 65 is thus slidably secured on the stem 62' of thepiston 1600 to permit the piston head 65 to move axially upwardly withrespect to the stem 62 on its shank 64 from the downwardly extendedposition of the said piston head 65 shown in Fig. 6. a

The upper annular portion 651 of the piston head 65 seats against thecurved contact annulus 56 of the S-shaped piston ring 50, and an axiallydisposed beveled seat 610 formed at the lower end of the main portion61of the piston 1600 is normally in contact with the curved contactannulus 57 of the piston ring 50. With such an arrangement of elements,movement of the piston head 65 axially upwardly from its position shownin Fig. 6 expands the said S-shaped piston ring 50 radially. The head 65of the piston 1600 is provided with longitudinal bores 652 therethroughto provide communication between the cylinder 15 below the piston 1600and an-annular pressure chamber '500 within the piston ring 50 betweenthe outer annular free wall 53 and the central annular wall 55 thereof.The upper end of the piston head 65 is provided with an upwardlydisposed annular lip 653 spaced radially from the outer periphery of thesaid piston head 65. The said annular lip 653 is formed to cam or urgethe depending edge 54 ofthe outer annular free wall 53 of the pistonring 50 radially outwardly against'theinner periphery'of the cylinderwhen the said piston head 65 moves upwardly as viewed'in Fig. 6.

With the construction shown inFigs. 6 and 7,' when the piston 1600 is onits power stroke, pressure from molten metal at the. head 65 thereofenters andflows through the. bores 6 52 therein into the annularpressure'chaniber 500 between the outer annular free wall 53 and'thecentral annular wall 55 of the piston ring 50 urgingithefree wall 53 ofthe said piston ring 50 outwardlyin firmsurface contact with the wall ofthe cylinder .15. Simultaneously, pressure from molten metal on the head65 of the piston 1600 urges the said. piston head upwardly as viewed inFig. 6 whereupon the annular portion 651 .of the piston head-65 contactsthe-contact annulus 56 .of the piston ring 50 forcing the contactannulus 57 .of .the said piston ring 50 against the-axially disposedbeveled.-s'eat.610 of the mainportion 61 of the piston 1600. Thislocalized axial Squeezing force on the piston ring 50 tends tomechanically expand it radially to further tighten the sliding .seal'between the outer free wall 53 of the piston ring 50-andthe inner .wallof the cylinder 15.. During the return stroke of the piston 16, thepressurewithin the; said annular pressure chamber 500 is relieved andthe pressure tending to mechanically expand the piston ring 50 radiallyis also relieved whereupon the outer free wall- 53 of the piston ring 50may flex .radially inwardly and permit molten metal to be sucked pastthe piston 1600 and the piston ring 50 without-undue abrasion anderosion of the saidpiston ring and the cylinder 15.

Obviously more thanone piston ring may be employed on a single pistonwhenever the requirement for a plurality of piston rings on a singlepiston is indicated, In such event, the piston will be altered. indetail to accommodate more than one piston ring, ,Howevenbecause oftheefliciencyof piston rings embodying the invention,

the use of more than one piston ring ona single piston would beunnecessary in most installations.

Although several embodiments of the invention have been disclosed anddescribedherein, it is obvious that many changes may be made in thesize, shape, arrangement and detail of the various elements of theinvention, all without departing from the spirit and scope thereof asdefined by the appended claims.

I claim: 4

I 1. In a piston reciprocable in a'cylinder and having a circumferentialrecess therein, a continuous piston ring of a laterallyflanged'U-sha'ped cross section disposed in said recess forming anannular pressurechamber between said piston ring and said piston at saidrecess there'irnthe said piston'having a communicating passage thereinbetween the head of said piston and said pressure chamber, a portion ofsaid piston head being axially movable responsive to fluid pressurethereon to apply mechanical pressure to the flanges of said U-shapedpiston ring and bulge the bottom wall thereof against the wall of saidcylinder.

2. In a piston having a circumferential recess therein, a continuouspiston ring of S-shaped cross section disposed in said recess forming anannular pressure chamber between said piston ring and said piston, thesaid piston having a communicating passage therein between the head ofsaid piston and said pressure chamber.

3. In a piston reciprocable in a cylinder, said piston including a mainportion and an axially movable head, the said piston having acircumferential recess therein with the said axial movable head formingone wall of said recess, a piston ring disposed in said recess formed toprovide an annular pressure chamber between said piston ring and saidpiston, the said piston having a communicating passage therein betweenthe head of said piston and said pressure chamber, said axially movablepiston head being arranged to grip said piston ring responsive to axialfluid pressure applied on said piston head and bulge an annular wall ofsaid piston ring into contact with the wall of said cylinder.

6 .:4..In-alpistoii-reciprocable in a. cylinder, said piston including.a. main. portion and an axially movable head, the. said piston .havinga. circumferential recess therein with the. said axialmovableheadforming one wall .of said recess, a 'U-shaped piston ring havingoutwardly flanged side wallsand a bottom cylinder contacting walldisposed in said recess to provide an annular'pressure chamber between.said piston. ring and said piston, the said pistonhavinga communicatingpassage therein between the head of said piston. and said pressurechamber, saidaxially movable piston head. being arranged to grip theflanges said -U-shap.ed pistonring between the main portionihereof .andsaid .head and bulge said bottom 9Y1. inder contacting wall thereof intocontact with the wall of saidcylinder, the said bottom cylinder.contacting wall of said u-shaped piston ring having a groovetherearoundwhereby to provide an annular area of greater flexibilitythan theremainder of said pistonring', fluid under pressure insaid. annularpressure chamber acting to urge said bottom cylinder contacting wall ofsaid U-. shaped. piston. ring into firm contact with said cylinder when.said piston is on its .compression stroke. 5. In a piston reciprocablein a cylinder, said piston including. a main portion and an, axiallymovable head and having. a circumferential recess therein with the saidaxialmovable head forming one wall of said recess, a continuous pistonring disposed in said recess formed to provideaan annular pressurechamber between said piston .ring and said piston, the said pistonhaving a communicatingv passage therein between its head and saidpressure chamber through which fluid under pressure against said pistonhead during the pressurestroke of said piston-enters said pressurechamber and forces an annular. Wall of saidpiston ring against thewallof said cylinder whereby to establish firm contact between. saidpistonringand the wall of said cylinder during the said pressure strokevof .said piston, said piston ring being formed for engagement by saidaxial movable head to bulge \mechanically. responsive to fluid pressurein said cylinder thereby increasing the said firmness of contact of thepiston ring against said cylinder wall.

6'..-In a pistonreciprocable in a cylinder, said piston including a mainportion and an axially movable head and having a circumferentialrecesstherein with the said axiallmovablehead forming one wall of saidrecess, a continuous resilient metallic U-shaped piston. ring disposedin said. recessformed to provide an annular pressure. chamber betweensaid piston ring and said piston, the, .said piston having acommunicating passage therein between its head and said pressure chamberthrough which fiuid under pressure against said piston head during thepressure stroke of said piston enters said pressure chamber whereby tourge said piston ring wall into firm contact with the wall of saidcylinder during the said pressure stroke of said piston, said U-shapedpiston ring including flanges axially disposed between and contacted bysaid main portion and said movable head of said piston whereby saidpiston ring is axially squeezed mechanically responsive to fluidpressure on said movable head to further urge said piston ring wall intofirm contact with the wall of said cylinder during the power stroke ofsaid piston.

7. The construction claimed in claim 6 wherein the outer peripheral wallof said continuous piston ring is grooved to assure radially outwardflexing of said piston ring against said piston ring during the powerstroke of said piston.

8. In a piston reciprocable in a cylinder, said piston including a mainportion and an axially movable head and having a circumferential recesstherein with the said axial movable head forming one wall of saidrecess, a continuous S-shaped piston ring disposed in said recess formedto provide an annular pressure chamber between said piston ring and saidpiston, the said piston having a communicating passage therein betweenits 7 head and said pressure chamber through which fluid under pressureagainst said piston head during the pressure stroke of said pistonenters said. pressure chamber and forces the outer annular wall'of saidS-shaped piston ring against the wall of said cylinder whereby to urgesaid piston ring wall into firm contact with the wall of said cylinderduring the said pressure stroke of said piston, the said outer annularwall of said S-shaped piston ring having a free annular edge disposedtoward said axially movable head of said piston, the said movable headof said piston including an annular lip formed to engage said freeannular edge of said S-shaped-piston ring and earn the same against thecylinder wall during the pressure stroke of said piston.

9. The construction claimed in claim 9 wherein the outer periphery ofthe main portion of said piston is axially beveled at said recess insaid piston whereby to engage the axially disposed annular portion ofsaid S-shaped piston ring axially spaced'from the said free anular edgethereof and additionally urge the outer annular wall of said S-shapedpiston ring radially outwardly into firm contact with said cylinder wallduring the pressure stroke of said piston.

10. In a piston reciprocable in a cylinder, said piston including a mainportion and an axially movable head, the said piston having acircumferential recess therein with the said axial movable head formingone wall of said recess, a continuous resilient metallic generally U-shaped piston ring disposed in said recess formed to provide an'annularpressure chamber between said piston 9 ring and said piston, the saidpiston having a communicating passage therein between the head of saidpiston and said pressure chamber, flanges outwardly extending from saidU-shaped piston ring grippable between said main portion and the axiallymovable portion of said piston head responsive to axial pressure appliedon said piston head during the compression stroke thereof where by tobulge the annular wall of said U-shaped piston ring adjacent saidcylinder into contact with the wall of said cylinder.

11. In a piston reciprocable in a cylinder, said piston including a mainhead portion and an axially movable head portion with a circumferentialrecess formed between the said head portions, a continuous resilientmetallie generally U-shaped piston ring disposed in said recess formedto provide an annular pressure chamber between said piston ring and saidpiston, the said piston having a communicating passage therein betweenits head and said pressure chamber through which fluid under pressureagainst said piston head during the compression stroke of said pistonenters said pressure chamber and forces the annular wall of saidU-shaped piston ring against the wallof said cylinder whereby toestablish firm contact between said piston ring and the wall of saidcylinder during the said compression stroke of said piston, said axiallymovable head portion of said piston being movable against a portion ofsaid piston ring responsive to fluid pressure on said movable head toflex said piston ring wall mechanically and increase its firmnessofvcontact with said cylinder wall.

12. In a piston ring and piston construction for use in die castingmachine pressure chambers, a cylinder in which said piston reciprocatesto move molten metal under high pressures, the said piston having acircumferential piston ring recess therein bounded by oppositelydisposed axial facing walls, one of said walls being fixed and the otheraxially movable, the piston body forming the said fixed wall of saidrecess, an axially movable head on said piston forming the axiallymovable wall of said recess, an annular cup shaped continuous pistonring positioned in said piston recesshavingaxially extending flanges atthe inner periphery thereof and a flexible wall disposed between saidflanges and adjacent the wall of the cylinder in which said pistonreciprocates, the said fixed and movable axially facing walls definingsaid piston ring recess normally contacting the axially extendingflanges of said piston ring, the said piston having a molten metalpassage therein through said piston head and communicating with saidpiston ring recess and within said annular cup shaped piston ring, saidflexible wall of said piston ring being expandible radially outwardlyinto positive sealed relationship with the wall of said cylinderresponsive simultaneously to hydraulic pressure of molten metal fromwithin said piston ring and mechanical pressure against the axiallyextending flanges of said piston ring, said mechanical pressure beingcreated by hydraulic pressure of molten metal against said axiallymovable piston head.

References Cited in the file of this patent UNITED STATES PATENTS

